Background grid warping when zooming in User Persp
This is a normal wide-angle perspective distortion. To reduce it, you need to look at your subject through a longer lens from further away. 

Bring up your right-hand panel (hotkey N) find the 'view' section, and change the 'lens' length to a higher number, and track back using the middle mouse wheel.

The longer the lens, and the further away you pull back the camera, the more closely the view will approximate to orthogonal, just as in real-life photography.